Weather Service Report


851 
FXUS66 KPQR 280505
AFDPQR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PORTLAND OR 
843 PM PST THU NOV 27 2014

.SYNOPSIS...A FRONTAL ZONE REMAINS STALLED OVER WESTERN OREGON AND
WILL REMAIN SO THROUGH FRIDAY. ANOTHER UPPER LEVEL DISTURBANCE WILL
RIDE ALONG THE FRONT LATER TONIGHT AND EARLY FRIDAY...LIKELY CAUSING
RAIN TO FILL IN AGAIN ACROSS THE FORECAST AREA. A SHARP COLD FRONT
WILL MOVE SOUTHEAST ACROSS THE REGION FRIDAY NIGHT. THERE WILL BE A
SHARP TEMPERATURE DROP WITH THE PASSAGE OF THIS COLD FRONT...WITH
SNOW LEVELS QUICKLY LOWERING OVERNIGHT. MIXED RAIN/SNOW SHOWERS ARE
EXPECTED IN THE LOWLANDS SATURDAY AS AN UPPER TROUGH PASSES THROUGH.
SNOW ACCUMULATIONS SHOULD BE LIMITED TO THE HILLS AND ABOVE. HIGH
PRESSURE WILL SETTLE IN EAST OF THE CASCADES SATURDAY NIGHT AND
SUNDAY... BRINGING STRONG EAST WINDS THROUGH THE GORGE AND ACROSS THE
PORTLAND METRO AREA. A SYSTEM COMING UP FROM THE SOUTH MAY ATTEMPT TO
SPREAD MOISTURE UP OVER THE COLD AIR EARLY NEXT WEEK... BUT AT THIS
POINT IT APPEARS MOST PRECIPITATION WILL STAY SOUTH OF OUR FORECAST
AREA. 

&&

.SHORT TERM...TONIGHT THROUGH SUNDAY...IT IS A MILD AND RAINY NIGHT.
THIS KIND OF WEATHER CONTINUES FOR ANOTHER DAY THEN MORE WINTER LIKE
WEATHER.

PATTERN HAS CHANGED LITTLE TODAY WITH ONE STALLED FRONT OVER SW
OREGON AND NORTHERN CALIFORNIA BRINGING STEADY RAIN ACROSS LANE AND
LINN COUNTIES.NORTH OF THAT MORE SCATTERED SHOWERS CONTINUE BUT
WITH DECENT SW FLOW IN THE MID LEVELS THE OREGON CASCADE ZONES
ACCUMULATED AROUND 0.25 TO 0.5 INCH OVER THE PAST 6 HOURS. THE COAST
RANGE HAD ABOUT HALF THAT. FURTHER NORTH OVER WESTERN WA ANOTHER
FRONT IS SLOWLY MOVING TO THE SOUTH.  THIS FRONT BECOMES DOMINANT
OVERNIGHT AND FRI THEN SLIDES INTO SW WASHINGTON AND NW OREGON FRI
AFTERNOON AND NIGHT AND WILL USHER IN THE COLDER WEATHER.  MODELS
INDICATE THIS WILL BE A SHARP FRONT. 00Z NAM AND GFS SHOWS TIGHT
THICKNESS/TEMPERATURE PACKING UP TO 700 MB. NAM FRONTOGENSIS IS
STRONG UP THROUGH 850 MB. THIS WOULD INDICATE DECENT LIFT AS THE
FRONT MOVES THROUGH. MODEL QPF AMOUNTS LOOKED TOO HIGH PREVIOUSLY
THROUGH FRIDAY BUT LOOK MORE REASONABLE NOW.  SO HAVE UPDATED QPF
AMOUNTS TONIGHT AND FRI.


PREVIOUS DISCUSSION...
12Z/18Z NAM BUFR SOUNDINGS SUGGEST SOME WEAK MOIST/CONDITIONAL
INSTABILITY AHEAD OF THE FRONT FRIDAY. WOULD NOT BE SURPRISED TO SEE
A COUPLE STRAY LIGHTNING STRIKES ALONG AND AHEAD OF THE FRONT...
ESPECIALLY CONSIDERING THE STRONG FRONTOGENETICAL LIFT ASSOCIATED
WITH THE FRONT. HOWEVER...INSTABILITY IS EXTREMELY MARGINAL SO WE
DECIDED TO LEAVE IT OUT OF THE FORECAST AT THIS POINT...CHANCES ARE
PROBABLY AROUND 5-10 PERCENT FOR ANY GIVEN LOCATION.

SNOW LEVELS ARE PRESENTLY VERY HIGH...WITH TIMBERLINE WEBCAMS SHOWING
RAIN AS HIGH AS 6000-7000 FT ELEVATION. IT WILL BE A MUCH DIFFERENT
STORY FRI NIGHT AS SNOW LEVELS RAPIDLY LOWER BEHIND THE FRONT. 12Z
ECMWF SHOWS 925 MB TEMPS CRASHING FROM +9 DEG C LATE FRI AFTERNOON TO
-1 DEG C SIX HOURS LATER. BY OUR STANDARDS...THAT IS A FAIRLY
IMPRESSIVE DROP. AT THIS POINT...MOST MODEL SOUNDINGS SEEM TO SUPPORT
SOME WET SNOWFLAKES REACHING THE NORTH COAST AND VALLEY FLOOR BY
SATURDAY MORNING. SHALLOW INSTABILITY CONTINUES THROUGH THE DAY
SATURDAY A POSITIVELY TILTED UPPER TROUGH MOVES THROUGH THE PAC NW.
GIVEN 850 MB TEMPS IN THE -7 TO -8 DEG C RANGE...HEAVIER SHOWERS MAY
STILL PRODUCE A MIX OF RAIN AND WET SNOW OR GRAUPEL DOWN TO THE
VALLEY FLOOR. HOWEVER IT APPEARS ACCUMULATING SNOW WILL BE LIMITED TO
ELEVATIONS ABOVE 500 TO 1000 FT...WITH ACCUMULATIONS INCREASING WITH
ELEVATION ABOVE THAT. THE HIGHER WEST HILLS OF PORTLAND AND SOME
HIGHER ELEVATION SUBURBS MAY SEE A SLUSHY INCH OR TWO OF ACCUMULATION
BY THE TIME ALL IS SAID AND DONE. SNOW LEVELS WILL BE A LITTLE HIGHER
FURTHER TO THE SOUTH. 

HIGH PRESSURE WILL THEN BUILD IN SATURDAY NIGHT...BECOMING MORE
CENTERED EAST OF THE CASCADES BY SUNDAY. OFFSHORE PRESSURE GRADIENTS
WILL INCREASE SUNDAY...WITH SOME HIGH RESOLUTION MODELS SUGGESTING
KTTD-KDLS PRESSURE GRADIENTS WILL GET TO -10 MB OR POSSIBLY STRONGER.
THIS WOULD BE ENOUGH FOR EAST WINDS GUSTING 60-70 MPH THROUGH THE
GORGE...AND 40-45 MPH GUSTS IN THE PORTLAND METRO AREA. IF MODELS
CONTINUE THIS TREND...A WIND ADVISORY MAY EVENTUALLY BE NEEDED FOR
THE PORTLAND/VANCOUVER METRO. TEMPERATURES WILL BE WELL BELOW NORMAL
SAT/SUN...WITH HIGHS STUCK IN THE 30S IN AND NEAR THE GORGE AND 40S
MOST LOWLAND LOCATIONS ELSEWHERE.  WEAGLE
 
.LONG TERM...SUNDAY NIGHT THROUGH THURSDAY...STRONG EAST WINDS SHOULD
EASE SOMEWHAT MONDAY AS A NORTHERN STREAM SYSTEM AND ASSOCIATED
WESTERLY FLOW ALOFT SHOULD ERODE THE HIGH PRESSURE CENTER EAST OF THE
CASCADES. THIS SHOULD CUT DOWN THE PRESSURE GRADIENT A BIT...THOUGH
SOME SORT OF EASTERLY FLOW SHOULD LINGER INSIDE THE GORGE. THERE IS A
LOT OF UNCERTAINTY IN REGARDS TO AN UPPER LEVEL LOW WHICH IS FORECAST
TO CUT OFF SOMEWHERE WEST OF CALIFORNIA SUNDAY. THE 12Z/18Z GFS HAVE
BEEN OUTLIERS IN COMPARISON TO THE LAST COUPLE RUNS OF THE ECMWF AND
THE 12Z CANADIAN MODEL...IN BRINGING A SIGNIFICANT BATCH OF
PRECIPITATION BACK NORTHWARD ACROSS OREGON SUN NIGHT/MONDAY THEN
HAVING IT LINGER FOR MUCH OF THE WEEK. MEANWHILE THE LAST COUPLE RUNS
OF THE ECMWF AND GEM KEEP US GENERALLY DRY THROUGH MIDWEEK...WITH
ANOTHER MODERATE SURGE OF EAST WIND TUE/WED. AFTER COLLABORATING WITH
NEIGHBORING OFFICES...THERE WAS A LARGE CONSENSUS THAT THE GFS
SOLUTION SHOULD BE DISCOUNTED FOR NOW...WITH OUR FORECAST FOLLOWING
MORE IN LINE WITH THE 12Z ECMWF SOLUTION. HOWEVER...IF MODELS START
TO TREND MORE TOWARD THE CURRENT GFS SOLUTION...WE MAY NEED TO
CONTEND WITH SNOW OR ICE FOR AT LEAST A PORTION OF THE COLUMBIA
GORGE.WEAGLE 

&&

.AVIATION...FRONTAL BOUNDARY THE INTERIOR HAS REMAINED LARGELY
STATIONARY WITH MIX OF MVFR/VFR CIGS OVER THE INTERIOR THIS
EVENING AS LOWER CLOUD DECKS SOMEWHAT VARIABLE. MEANWHILE...MVFR
CONDITIONS CONTINUE FOR THE COASTAL AREAS. EXPECT BOUNDARY WITH
CONSIDERABLE LOW LEVEL MOISTURE TO REMAIN OVER THE REGION...SO
EXPECT TRENDING TOWARD INCREASINGLY MVFR CIGS OVER THE REGION
THROUGH THE OVERNIGHT PERIOD ALONG WITH INCREASING PRECIP
INTENSITY THROUGH FRI MORNING...AND HEAVIER RAIN MAY BRING VSBY
RESTRICTIONS TO THE 3-5 SM RANGE. A STRONG COLD FRONT APPROACH
THE REGION ON FRI...BRINGING A SHIFT TO NW WINDS TO NORTHERN
PORTION OF THE AREA AROUND 18Z FRI...REACHING THE SOUTHERN
PORTIONS BY 06Z SAT. HIGHER TERRAIN...SUCH AS THE OREGON COAST
RANGE...SW WA WILLAPA HILLS AND THE CASCADES WILL REMAIN OBSCURED
THROUGHOUT THE PERIOD.

KPDX AND APPROACHES...MIX OF MVFR/VFR CONTINUES AT THE TERMINAL
AND APPROACHES WITH CIGS 2500-3500 FT RANGE. LITTLE CHANGE
EXPECTED THROUGH FRI. S WINDS CONTINUE OVERNIGHT...SHIFTING TO
W-NW BEHIND THE FRONT BETWEEN 00Z-03Z SAT. CULLEN

&&

.MARINE...LATEST MODEL GUIDANCE AND OBSERVATIONS CONTINUE TO
SUGGEST GUSTS TO 25 KT AT TIMES THROUGH FRI MORNING. THERE MAY BE
SHORT PERIODS OF SUB-ADVISORY WIND SPEEDS THROUGH TONIGHT...BUT
BELIEVE THIS WILL BE THE EXCEPTION INSTEAD OF THE RULE. FAVOR THE
NAM/GFS WIND FIELD THROUGH SAT. A MORE ROBUST COLD FRONT WILL MOVE
SOUTH THROUGH THE COASTAL WATERS LATE FRI AND EARLY FRI EVENING
FOR CONTINUED SMALL CRAFT ADVISORY WIND. THE WIND WILL SWITCH TO
THE NORTHWEST BEHIND THIS FRONT. THE NORTHWEST WINDS WILL EASE ON
SATURDAY...THEN OFFSHORE GAP ENHANCED EAST WINDS WILL DEVELOP
SATURDAY NIGHT AND SUNDAY...LIKELY EXCEEDING SMALL CRAFT ADVISORY
CRITERIA. THE OFFSHORE WIND CONTINUES INTO EARLY NEXT WEEK...BUT
FAVOR THE ECMWF WIND PATTERN. 

SEAS HOLDING IN THE 10 TO 13 FT RANGE AND WILL STAY THAT WAY THROUGH
EARLY FRIDAY...THEN CONTINUE TO HOVER AROUND 10 FT INTO
SATURDAY...BEFORE FALLING BELOW 10 FT BY SUNDAY. THE OFFSHORE
FLOW LATER THIS WEEKEND WILL DECREASE WAVE HEIGHT...BUT RESULT IN
VERY CHOPPY CONDITIONS. CULLEN/WEISHAAR

&&

.PQR WATCHES/WARNINGS/ADVISORIES...
OR...NONE.
WA...NONE.
PZ...SMALL CRAFT ADVISORY FOR WINDS UNTIL 8 AM PST SATURDAY FOR 
     COASTAL WATERS FROM CAPE SHOALWATER WA TO FLORENCE OR OUT 60 NM.

     SMALL CRAFT ADVISORY FOR HAZARDOUS SEAS UNTIL 8 AM PST SATURDAY 
     FOR COASTAL WATERS FROM CAPE SHOALWATER WA TO CASCADE HEAD OR
OUT 60 NM.

     SMALL CRAFT ADVISORY FOR HAZARDOUS SEAS UNTIL 10 PM PST FRIDAY 
     FOR COASTAL WATERS FROM CASCADE HEAD OR TO FLORENCE OR OUT 60
NM.

     SMALL CRAFT ADVISORY FOR ROUGH COLUMBIA RIVER BAR UNTIL 4 PM PST
FRIDAY.

&&

$$

INTERACT WITH US VIA SOCIAL MEDIA    
WWW.FACEBOOK.COM/NWSPORTLAND
WWW.TWITTER.COM/NWSPORTLAND

THIS DISCUSSION IS FOR NORTHWEST OREGON AND SOUTHWEST WASHINGTON 
FROM THE CASCADE CREST TO 60 NAUTICAL MILES OFFSHORE. THE AREA IS 
COMMONLY REFERRED TO AS THE FORECAST AREA.

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